1. Field
The present disclosure relates generally to communications systems, and more specifically, to system and method of companding an input signal of an energy detecting receiver.
2. Background
Communications devices that operate on limited power supplies, such as batteries, typically use techniques to provide the intended functionality while consuming relatively small amounts of power. One technique that has been gaining in popularity relates to receiving signals using pulse modulation techniques. This technique generally involves receiving information using low duty cycle pulses and operating in a low power mode during times when not receiving the pulses. Thus, in these devices, the power efficiency is typically better than communications devices that continuously operate a receiver.
Usually, energy detecting receivers are employed when using pulse modulation techniques. In such receiver, the input signal is typically applied to a non-linear device, such as a substantially squaring device, in order to detect the incoming pulses. However, the non-linear or squaring device generally increases the dynamic range of the input signal by a factor of two (2) as measured in decibels (dB). Because of the substantial increase in the dynamic range of the input signal, the power level of the input signal should be controlled in order to prevent compression or, conversely, falling below the sensitivity of subsequent receiving stages.
In the past, automatic gain circuits (AGC) have been employed in order to address the relatively large dynamic range of the input signal generated at the output of the non-linear or squaring device. In such application, the AGC circuit is configured to partition the dynamic range into several overlapping windows, and requires sophisticated and fast circuitry to maintain the received signal level within the proper window. For instance, if the wrong window is selected for the instantaneous level of the received signal, then information may be lost by either the receiver going into compression or conversely dropping below the receiver's sensitivity. Further to the speed and accuracy requirements of the AGC circuit, there is the requirement of the overlapping windows. To minimize overlap and therefore the number of AGC windows, tight receiver gain tolerances are typically required, which leads to complex, costly, and power consuming circuits.